The invention relates to switched reluctance ("SR") motors and particularly to an apparatus for determining which phase of an SR motor to commutate at a given moment.
SR motors have multiple poles on both the stator and the rotor. There are windings or coils on the stator poles and each pair of windings on diametrically opposite stator poles is connected in series to form an electrically independent phase of the SR motor. There are no windings or magnets on the rotor. However, the rotor is made of a magnetically permeable material such as, for example, a ferrous alloy.
In order to start an SR motor, it is necessary to determine the position of the rotor with respect to the stator. The position of the rotor with respect to the stator establishes which phase of the stator should be energized or commutated first. If the position of the rotor is not correctly determined, commutation of one of the stator phases may result in inefficient starting or reverse operation of the motor. However, many conventional sensors for determining rotor position are bulky, unreliable and expensive.